The background description provided herein is for the purpose of generally presenting the context of the present invention. The subject matter discussed in the background of the invention section should not be assumed to be prior art merely as a result of its mention in the background of the invention section. Similarly, a problem mentioned in the background of the invention section or associated with the subject matter of the background of the invention section should not be assumed to have been previously recognized in the prior art. The subject matter in the background of the invention section merely represents different approaches, which in and of themselves may also be inventions. Work of the presently named inventors, to the extent it is described in the background of the invention section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present invention.
The blood-brain barrier (BBB) acts as the gatekeeper between the central nervous system (CNS) and the rest of the body. It is the responsibility of the BBB to facilitate the entry of required nutrients into the brain and exclude potentially harmful compounds. However, this critical and complex structure remains difficult to model in vitro. Accurate in vitro models are necessary for understanding how the BBB forms and functions, for evaluating drug, toxin, and viral penetration across the barrier, and for recreating the BBB response and CNS response in disease models. Many existing in vitro models either fail to support all the cell types involved in BBB formation and/or do not provide the shear forces created by flow necessary for mature tight junction formation. While the transwell BBB with endothelial cells and astrocytes is a standard in the pharmaceutical industry, its shortcomings include the lack of shear-flow induced polarization of the endothelial cells; large, physiologically unrealistic fluid volumes; difficulty in supporting more than two cell types; and the inability to use electrical recordings to monitor neural activity in situ. There are a large number of different applications of biological barriers that are studied using transwell, including the endothelia/epithelial/air interface at the skin, the endothelial/epithelial interface within the pulmonary alveoli, the endothelial/epithelial interface in the lumen of the gastrointestinal tract, etc., that would benefit from lower fluid volumes and improved, shear-flow-induced polarization. Transwells also have widespread application as a cancer cell migration tool, wherein cells within the insert migrate across the barrier in response to chemical signals produced by cells growing at the bottom of the well. The ability of the cells in the insert to sense the signals from cells in the well is compromised by the dilution of signaling molecules and metabolites by the large fluid volumes in both the well and the insert.
Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies.